In the current Internet communication environment, Internet Protocol version 4 (IPv4) is used and on the Internet, only communication by IPv4 global addresses (globally unique, allocated addresses) is performed.
Nonetheless, consequent to the rising number of network connected terminals and the increasing need for protection against upsurges in the exploitation of terminal vulnerability, business and residential networks use private addresses that can be used only for communication within the local business or residential network. When communication with a counterpart terminal is performed via the Internet, typically, an address translation device is used and the private address is converted into a global address (network address translation (NAT)) (see, for example, Japanese Laid-Open Patent Publication Nos. 2002-204252 and 2000-156710). A global address and a port number can be uniquely allocated to connections equivalent to global address count×port number count.
Address translation, for example, in the case of businesses, is implemented at the boundary of the local business network and the Internet, and in the case of residences, is implemented at a broadband router setup in the residence.
In recent years, the extent to which the number of network connected terminals has increased is remarkable and it is predicted that available IPv4 addresses will be exhausted; a state of insufficient IPv4 global addresses for Internet communication is approaching.
Although address translation enabling multiple terminals to be consolidated to the same global address is effective, in the case of residences, since address translation is implemented by a broadband router, each residence is allocated 1 global address and consequently, address allocation is not very efficient.
Thus, rather than performing address translation by broadband routers setup in residences, carrier-grade NAT is known that implements address translation collectively at carrier providers such as Internet service providers (ISPs). Carrier-grade NAT is an approach of performing NAT on an extremely large-scale and of exclusively undertaking communication of all ISP subscriber terminals and performing address translation.
Nonetheless, even with carrier-grade NAT, the address translation scheme is identical to the NAT address translation scheme of implementing address translation by the broadband router at residences. Therefore, a paired global IP and port number are allocated for each communication (Transmission Control Protocol (TCP)/User Datagram Protocol (UDP) communication) and when the communication has ended, the global IP and port number are reallocated to another communication, making global address use efficient.
However, currently, the extreme rise in the number and types of terminals connecting to the Internet as well as the increase in the number of TCP connections used for one communication are posing problems. For example, for a personal computer (PC) user to merely view a Web page using browser, in the past, 1 TCP connection was used, however, recently, several hundred TCP connections may be used.
Consequent to the problem of increases in the quantity of global addresses used, a further problem arises in that sufficient improvement in the efficiency of global address use by an introduction of carrier-grade NAT cannot be realized (e.g., since there are 65,000 port numbers, when 65,000 TCP connections and UDP communications occur, other global IP addresses have to prepared).